The Pygmalion effect, or Rosenthal effect, is the phenomenon whereby others' expectations of a target person affect the target person's performance. The effect is named after the Greek myth of Pygmalion, a sculptor who fell in love with a statue he had carved, or alternately, after the Rosenthal–Jacobson study. Robert Rosenthal and Lenore Jacobson's study showed that, if teachers were led to expect enhanced performance from children, then the children's performance was enhanced. This study supported the hypothesis that reality can be positively or negatively influenced by the expectations of others, called the observer-expectancy effect. Rosenthal argued that biased expectancies could affect reality and create self-fulfilling prophecies.

Robert Rosenthal